#include<stdio.h>
int devide9(int num);
int decimal_binar(int num);
int binar_decimal(int num);
int main()
{
int menu, num9, numd1, numb1, numd2, numb2, numfinal1;
 
	printf("\nHallo these are your options:\n");
	printf("1. Check if your number can be devide by 9 without residue.\n");
	printf("2. Decimal - binar converter.\n");
	printf("3. Binar - decimal converter.\n");
	printf("4. Exit.\n");
	scanf("%i", &menu);
 
	switch (menu)
	{
		case 1:
			printf("please enter a number:\n");
			scanf("%i", &num9);
			numfinal1 = devide9(num9);
			if (numfinal1 == 9)
				printf("the number can be devided by 9.\n");
			else
				printf("the number can not be devided by 9.\n");
			main();
		case 2:
			printf("please enter a number:\n");
			scanf("%i", &numd1);
			numb1 = decimal_binar (numd1);
			if (numd1<0)
				printf("%i (base 10) => -%i (base 2)\n", &numd1, &numb1);
			else
				printf("%i (base 10) => %i (base 2)\n", &numd1, &numb1);
			main();
		case 3:
			printf("please enter a number:\n");
			scanf("%i", &numb2);
			numd1 = binar_decimal(numb2);
			if (numd2<0)
				printf("%i (base 2) => -%i (base 10)\n", &numb2, &numd2);
			else
				printf("%i (base 2) => %i (base 10)\n", &numb2, &numd2);
			main();
		case 4:
			return(0);
			break;
		default: main(); break;
 
	}
	return(0);
}
 
int devide9 (int num)
{ 
	int numT, num1;
	if (num<0)
		num = num*-1;
	numT = 0;
	while (num > 0 );
	{
		num1 = num%10;
		numT = num1 + numT;
		num = num/10;
	}
	if (numT>9)
		numT = devide9 (numT);
	return (numT);
}
 
int decimal_binar (int num)
{	
	int counter, multi, i, numT, num1, numd1;
	if (num<=1023 && num >= -1023)
	{
	if (num<0)
		num = num*-1;
	counter = 0;
		numT = 0;
		while (num > 0 );
		{
			num1 = num % 2;
			num = num / 2;
			if (counter == 0)
				numT = num1;
			else
			{
				multi = 1;
				for (i=1; i<=counter; i++)
				{
					multi = 10 * multi;
				}
			}
			numT = multi * num1 + numT;
			counter = counter +1;
		}
	}
	else
	{
			printf("please enter a new number:\n");
			scanf("%i", &numd1);
			numT = decimal_binar(numd1);
	}
	return (numT);
}
 
 
int binar_decimal (int num)
{
	int num1, counter, hez1, hezT, i,numT, numb1;
	counter = 0;
	if (num >= -1111111111 && num <= 1111111111)
	{
		if (num < 0)
			num = num*-1;
		counter = 0;
		numT = 0;
		while (num > 0 );
		{
			num1 = num % 10;
			hez1 = hezT = 1;
			for (i=1; i<=counter; i++) 
			{
				hez1 = hezT;
				hezT = hez1*2;
			}
		numT = num1*hezT + numT;
		counter = counter + 1;
		num = num / 10;
		}
	}
	else
	{
		printf("please enter a new number:\n");
		scanf("%i", &numb1);
		numT = binar_decimal (numb1);
	}
	return (numT);
}